This invention relates to a method of resin-sealing an electric part that includes a vibrating part, in which the vibrating part (serving as a vibration source for producing a push operating feeling), which is fixedly secured to a touch panel, is sealed at its outer surface with a resin.
And this invention relates to a screen-printing metal mask plate used for resin-sealing the outer surface of the electronic part, mounted on a board, by screen-printing.
Moreover, the present invention concerns a metal mask plate used for resin sealing an electronic part mounted in a periphery of a transparent operating area of a touch panel.
A touch panel input device is also called a digitizer, in which when an operating area, provided on a touch panel, is pushed or operated by a stylus pen or a finger, the pushed position within this operating area is detected, and input position data, representing the pushed position, is outputted to a processing apparatus such as a personal computer.
There are known various touch panel input devices which are classified into the contact type (as disclosed in JP-UM-A-3-6731), the resistance type ((as disclosed in JP-A-5-53715) and others, depending on a method of detecting a pushed position. In any of these types, when a pushing operation was effected, a clear pushing operation feeling, such as a click feeling obtained in a push button switch, was not obtained, and therefore the operator could know the results of the operation only through the processing apparatus such as a personal computer, and therefore the operator was anxious about whether or not the pushing operation on the operating panel was recognized.
Therefore, the present Applicant has developed a touch panel input device in which piezoelectric plates serving as vibrating parts are fixedly secured to a touch panel so as to efficiently vibrate the touch panel without forming the whole of the device into a large size, thereby transmitting a pushing operation feeling to the operator (see Patent Literature 1).
Patent Literature 1: JP-A-2003-122507 Publication (Abstract, FIG. 1)
An electronic part (such as a piezoelectric substrate), mounted on a board such as a touch panel, has electrodes (such as drive electrodes) exposed to a surface thereof, and therefore is susceptible to aged deterioration by oxidation, sulfurization or the like. And besides, there is a fear that the short-circuiting develops between the electrodes and also between the electronic part and other conducting part, and therefore generally, the whole of the electronic part is sealed with an insulative resin.
As a related resin-sealing method of sealing an electronic part with a resin, there are known a sealing method, employing a dispenser, and a screen-printing method employing a metal mask plate (see Patent Literature 2 and 3).
Patent Literature 2: JP-B-6-95594 Publication (Page 3, FIG. 2)
Patent Literature 3: Japanese Patent No. 3128612 (Page 2, FIG. 9)
In the former sealing method employing the dispenser, a sealing resin 214 is extruded by the use of a pneumatically-operated dispenser 205, and is coated on an electronic part 220 (which is to be sealed) to completely cover an entire outer surface thereof as shown in FIG. 9, and thereafter a panel, having the electronic part 220 mounted thereon, is passed through a heating surface, so that the sealing resin is thermally set or cured, and is fixed to the outer surface of the electronic part 220 to seal the same.
In the latter method, that is, the screen-printing method, a sealing resin is deposited on an outer surface of an electronic part as if the sealing resin were ink in the screen-printing. As shown in FIG. 10 and 25, a support base plate 202 (302), having the electronic part 220 (320) mounted thereon, is covered with the metal mask plate 212 (303) having a through hole 211 (305) which is slightly larger and deeper than a contour of the electronic part 220 (320) formed therein by etching or the like, and a squeegee 213 (304) is slid over the surface of the metal mask plate 212 (303), thereby filling the sealing resin 214 (306) in a gap between the through hole 211 (305) and the electronic part 220 (320).
Thereafter, the metal mask plate 212 (303) is removed, the sealing resin 214 (306), deposited on the outer surface of the electronic part 220 (320), is thermally set as in the former method, so that the sealing resin 214 (306) is fixed to the outer surface of the electronic part 220 (320) to seal the same.
In the sealing method using the dispenser, the sealing resin 214 need to be extruded through a narrow nozzle, and therefore the sealing resin 214 is limited to a low-viscosity type. When this sealing resin was coated on the surface of the electronic part 220, the coated sealing resin could not retain its shape until it was thermally set, and therefore in the case where there is used the plate-like electronic part such as the piezoelectric substrate, edge portions thereof were exposed, thus inviting a problem that the electronic part 220 could not be completely sealed. And besides, the process of completely depositing the sealing resin on the entire outer surface of each single electronic part 220 was complicated, and it was difficult to automate this process.
In the screen-printing method, the metal mask plate 212 (303) can be reused, and all of the electronic parts to be fixed to the supporting board (the touch panel) 202 (302) can be simultaneously resin-sealed, and therefore this method is suited for mass-production, and besides since the process is simple, this method is suited for automation. However, when using this method in an unchanged manner as means for resin-sealing the electronic part (the vibrating part such as the piezoelectric substrate) of the touch panel input device, there have been encountered-the following problems.
As shown in FIG. 25, the piezoelectric substrates (that include the vibrating parts) 320 to be fixed to the touch panel 302 are fixed to a region between the periphery of the operating area 300A and the peripheral edge of the touch panel 302 so that these piezoelectric substrates 320 will not hinder the detection of a pushed position. In order that a pushing operation can be easily effected for the touch panel 302 having a limited size to meet the requirements for a mounting space, a compact design, etc., (and that a display, disposed internally of the operating area 300A, can be more clearly seen through the operating area 300A in the case where the operating area 300A is transparent), it is required to provide the enlarged operating area 300A, so that each piezoelectric substrate 320 is fixedly mounted on a region of a much limited width. On the other hand, the piezoelectric substrate 320 that has as large a size as possible within the limited mounting width are used in order to more effectively produce large vibrations. As a result, a distance d2 between the piezoelectric substrate 320 and the operating area 300A was as small as about 0.5 mm when the piezoelectric substrate 320 with a width of 2 mm was mounted on the touch panel.
A relatively-sufficient mounting space for the piezoelectric substrates 320 may, in some cases, be available, and even in such a case, when a coating of the sealing resin 306, sealing the piezoelectric substrate 320, is thick, the sealing resin 306 restrains the piezoelectric substrate 320 from vibrating, so that the piezoelectric substrate 320 fails to effectively serve as the vibration-generating source, and therefore it is necessary to reduce the thickness of the sealing resin.
In the case of resin-sealing the piezoelectric substrates 320 by the use of the screen-printing method, it is necessary that the small distance d2 should be substantially equal to a lower thickness limit of the sealing resin 306.
On the other hand, it is also necessary to cover at least the flat surface of the piezoelectric substrate 320 with the sealing resin 306, and therefore the height or depth of the through hole 305 should be set to a value (for example, 1 mm) larger than the height of the piezoelectric substrate 320. Therefore, even when trying to fill the sealing resin 306 in this gap by the use of the squeegee 304, there was encountered a problem that the sealing resin 306 could not be fully filled in this narrow deep gap to thus fail to reach the touch panel 302, so that the whole of the piezoelectric substrate 320 could not be completely sealed.
With respect to this problem, when the sealing resin 306 of a low viscosity is used, and is filled into this gap while increasing the pressure of inflow of the resin (i.e., the pressure of filling) by the squeegee 304, the sealing resin 306 reaches the touch panel 302. However, when thus filling the sealing resin 306 while increasing the pressure of inflow of the resin by the squeegee 304, even the sealing resin 306 to be deposited on the flat surface (upper surface) of the piezoelectric substrate 320 was wiped off, so that part of the flat surface was exposed. And besides, when the viscosity of the sealing resin 306 was lowered, there was encountered a problem that the sealing resin, deposited on the surface of the piezoelectric substrate 320, could not retain its shape until the sealing resin was thermally set by the heating furnace, and therefore the deposited sealing resin flowed to be deposited on the operating area 300A, and the edge portions thereof were exposed, so that the complete sealing could not be achieved.
And in this related resin-sealing method, the sealing resin 306 is filled in the through hole 305 by the use of the squeegee 304, and therefore a material with fluidity and viscosity is used as the sealing resin 306. Therefore, when the metal mask plate 303 is removed from the periphery of the electronic part 320, part of the sealing resin 306, deposited on an edge portion of the electronic part 320, adheres to an inner surface of the through hole 305, and is pulled as shown in FIG. 26. The metal mask plate 303 is completely separated from the electronic part, and the sealing resin is thermally set as shown in FIG. 27, and in this condition a horn-like projection 307, resulting from the residual sealing resin 306, is formed at the edge portion of the electronic part 320.
As a result, the appearance was degraded, and besides the horn-like projection 307 abutted against other parts, and prevented a high-density mounting design, and could cause incomplete insulation and contact.
Particularly in a touch panel input device in which a display panel, such as liquid crystal display elements, is provided in a stacked manner on a rear side of a transparent touch panel, when a horn-like projection 307 is formed on a piezoelectric substrate (fixed to the rear surface of the touch panel so as to vibrate this touch panel), the horn-like projection 307 abuts against the display panel, so that the display panel can not be disposed in proximity to the touch panel, and therefore the display panel can not be viewed clearly.
And besides, when the horn-like projection 307 abuts against the display panel, the vibration of the piezoelectric substrate is restrained, which has invited a problem that the touch panel cannot be vibrated at sufficient amplitude.
Moreover, with this related metal mask plate 303, when the board 302 is covered with the metal mask plate 303, and the sealing resin 306 is filled into the gap around the electronic part 320, the metal mask plate 303 and the board 302 cannot be completely brought into contact with each other. Therefore, there have been cases in which, as shown in FIG. 28, part 306a of the sealing resin 306 which leaked into a gap between the metal mask plate 303 and the board 302 remains along the surface of the board 302.
Particularly in a case where a transparent operating area 300A is set in the touch panel 302 of a touch panel input device to permit input operation while viewing a display on a display unit disposed inwardly of the touch panel 302, and the electronic parts 320 mounted on a periphery of the operating area 300A on the board, i.e., the touch panel 302, are resin sealed, there has been a problem in that the part 306a of the sealing resin 306 leaking along the touch panel 302 adheres on the operating area 300A, making it difficult to view the display on the display unit.
This phenomenon appears frequently and more noticeably, since the position where the electronic part 320 is mounted and the operating area 300A are close together, and the sealing resin 306 is inevitably filled by increasing the filling pressure when the sealing resin 306 is thoroughly filled in a narrow gap d2 between the through hole 305 and the electronic part 320. Consequently, the part 306a of the sealing resin 306 comes to adhere to the operating area 300A that is close.
In addition, since the metal mask plate 303 is used repeatedly at the time of mass producing touch panel input devices 300, there has occurred a problem in that the sealing resin 306 used in the screen-printing process and other dust remain by adhering to the surface of the metal mask plate 303 opposing the touch panel 302, and adhere to the region of the operating area 300A at the time of covering a new touch panel 302, thereby impairing transparency.